1. Field of the Invention
This invention relates to devices which indicate the amount of relative movement between two points in various engineering, construction and mining applications and more particularly to such a device which gives a positive, dramatic indication of easily selectable amounts of such movement.
2. Prior Art
There are many applications in the engineering, construction and mining fields where it is desirable to be able to detect and measure relative movement between two points, such as the shifting of earth and rock formations, the sagging of mine roofs and the heaving in tunnels and deep excavations. Various devices have been proposed for these purposes. In U.S. Pat. No. 3,404,460, a rod anchored in a bore hole in the rock formation actuates a deflection type gauge or a potentiometer connected in an electrical indicating circuit to provide an indication of the internal movements in rock formations. In U.S. Pat. No. 3,416,320, a shaft connected to one anchor bolt secured deep in a bore in the wall of a tunnel or mine is freely slidable through another anchor bolt secured near the entrance of the bore. A plunger type gauge actuated by the rod measures the relaxation of the rock or earth formation. Also, in U.S. Pat. No. 3,460,258, a rod string anchored within an earth formation provides an indication of movement of the formation relative to a reference bushing adjustably positioned in a casing surrounding the upper end of the rod string. All of these above devices provide an analog indication of shifting of the earth or rock formation which requires careful reading to detect gradual shifting of the formation.
In U.S. Pat. No. 3,646,553, a housing containing a microswitch is biased against a mine roof by a spring which is restrained by a bracket clamped to the end of a cable or rod anchored in a bore in the mine roof. Displacement of the roof actuates a microswitch which completes a warning circuit. While this device provides a discrete warning of a preset displacement of a mine roof, it requires electric power supplied by batteries which require periodic charging or replacement. Like the other devices discussed above, it also requires an anchor which makes it more difficult to transfer the device from one position to another and is not adaptable to some applications. For instance, in spanning type foundations it is desirable to monitor the soil beneath the foundation for settlement. The above-mentioned devices are not suitable for this purpose.
A device has also been suggested in which a rod biased to follow one point pulls a plug out of a housing secured to the second point when the two points have opened a preset amount. However, such a device only indicates opening movement and when placed in a floor to detect settlement under a spanning type foundation, the plug can be accidently kicked out. Furthermore, it does not give as dramatic and easily recognizable indication of a preset amount of movement as is desirable.
It is a primary object of the present invention to provide a movement indicator which presents a discrete, easily readable mechanical indication of a predetermined amount of movement between two points.
It is another object of the invention to provide such a device in which the amount of movement required to actuate the discrete mechanical indication is readily selectable with the device in place.
It is also an object of the invention to provide such a device which offers a continuous analog presentation of the amount of movement in addition to the discrete indication of a preset shift.
It is a further object of the invention to provide a device as described above which can be adapted to provide an indication of either converging or diverging movement between two points.
It is yet another object of the invention to provide a device such as described above which can be used with or without anchors.
It is still another object of the invention to provide a device such as described above which can be easily removed and replaced after the void left by settlement has been filled with grout introduced through the opening accommodating the movement indicator.
It is finally an object of the invention to provide a device as described in the previous objects which is rugged, reliable and inexpensive to construct.